P0108 -What Does It Mean? (1999-2006 V8 Silverado, Sierra, Suburban, Tahoe, Yukon)

There are three possible MAP sensor trouble codes that can light up the check engine light on your Chevrolet Silverado (Suburban, Tahoe) and GMC Sierra (Yukon, Yukon XL) and the P0108: MAP Sensor Circuit High Voltage is one of them.

In this tutorial, I'll explain what this trouble code means. I'll also talk about some of the tests you can perform to find its cause and solution.

You can find this tutorial in Spanish here: Código P0108 ¿Qué Significa? (1999-2006 V8 Silverado, Sierra, Suburban, Tahoe, Yukon) (at: autotecnico-online.com).

APPLIES TO: This tutorial, on the P0108 OBD II trouble code, applies to the following vehicles:

Chevrolet:

• Silverado (1500, 2500):
  • 4.8L, 5.3L: 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006
• Silverado (2500):
  • 6.0L: 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006
• Suburban (1500):
  • 5.3L: 2000, 2001, 2002, 2003, 2004, 2005, 2006
• Suburban (2500):
  • 6.0L: 2000, 2001, 2002, 2003, 2004, 2005, 2006
• Tahoe:
  • 4.8L, 5.3L: 2000, 2001, 2002, 2003, 2004, 2005, 2006

GMC:

• Sierra (1500, 2500):
  • 4.8L, 5.3L: 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006
• Sierra (2500):
  • 6.0L: 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006
• Yukon:
  • 4.8L, 5.3L: 2000, 2001, 2002, 2003, 2004, 2005, 2006
• Yukon XL (1500):
  • 5.3L: 2000, 2001, 2002, 2003, 2004, 2005, 2006
• Yukon XL (2500):
  • 6.0L: 2000, 2001, 2002, 2003, 2004, 2005, 2006

RELATED TROUBLE CODES:

• P0106 -What Does It Mean? (1999-2006 V8 Silverado, Sierra, Suburban, Tahoe, Yukon).
• P0107 -What Does It Mean? (1999-2006 V8 Silverado, Sierra, Suburban, Tahoe, Yukon).

What Does Trouble Code P0108 Mean?

The fuel injection computer is programmed to predict what the MAP signal voltage should be based on engine RPM and the input of the throttle position sensor (TPS).

At key on but engine off (KOEO), the fuel injection computer predicts and expects to see a high signal voltage value from the MAP sensor.

Once the engine starts and it's idling (throttle plate is at rest and engine RPM are low), the fuel injection computer knows that the MAP signal voltage should be a low value.

As you step on the accelerator pedal, the throttle plate opens and engine RPM increase, the fuel injection knows the MAP signal voltage should increase.

When the actual MAP signal voltage stays excessively high as the throttle plate closes and engine RPM decrease, and does not match the voltage the fuel injection computer has predicted, a trouble code P0108: MAP Sensor Circuit High Voltage is set.

Common Symptoms Of A P0108 Trouble Code

When the MAP sensor signal voltage stays stuck at an excessively high value, that does not match the actual intake manifold pressure, engine performance will suffer.

You'll see one or more of the following symptoms:

• Check engine light illuminated.
• Rough or low idle.
• Very high idle.
• Engine may start and stall.
• Little to no acceleration.
• Black smoke comes out of the tailpipe when the engine is running.

What Does The MAP Sensor Do?

The MAP sensor has two specific jobs. The first is to provide the fuel injection computer with a barometric pressure reading when you turn the key on but before you start the engine.

The other, is report the engine load by measuring the intake manifold vacuum pressure as the engine runs.

When the engine is idling and the throttle plate is closed, intake manifold pressure is high.

This high intake manifold pressure will cause the MAP sensor to produce a low voltage signal (usually around 2 Volts DC).

As you step on the accelerator pedal, the throttle plate opens and the engine accelerates. This causes a decrease in intake manifold vacuum pressure.

This low intake manifold pressure will cause the MAP sensor to produce a high voltage signal. At wide open throttle (like when you trying to run that red light), the MAP sensor produces a voltage around 4 Volts DC.

As long as the MAP sensor voltage signal decreases/increases, as you step on or off the accelerator pedal, the fuel injection computer knows that the MAP sensor is functioning correctly.

What Causes A P0108 Trouble Code?

A bad MAP sensor is the most common cause of a P0108: MAP Sensor Circuit High Voltage trouble code, but unfortunately is not the only one.

Here are other causes of a P0108 trouble code:

• The MAP sensor signal wire has a short-circuit to voltage problem.
• A bad MAP sensor connector causing an intermittent false connection.
• The MAP sensor's vacuum inlet is plugged.
• The MAP sensor's Ground wire has an open-circuit problem between the MAP sensor connector and the PCM connector.
• Bad fuel injection computer (although a very rare problem).
• Major vacuum leak.

How To Diagnose And Repair A P0108 Trouble Code

To diagnose and repair a P0108 trouble code, you'll need to remove, inspect, and test the MAP sensor.

The test, which is done with a multimeter, will check to see if the MAP sensor signal voltage decreases/increases as you apply/release vacuum to sensor.

The test also verifies that the MAP sensor is getting 5 Volts and Ground from the fuel injection computer.

You can conclude that the MAP sensor is bad, and needs to be replaced, if your test results confirm:

• That the MAP sensor signal voltage DOES NOT decrease/increase as you apply/release vacuum to the sensor.
• That the MAP sensor is getting 5 Volts.
• That the MAP sensor is getting Ground.

I have written tutorial that will help you test the MAP sensor. You can find it here: How To Test The MAP Sensor (1999-2006 V8 Silverado, Sierra, Suburban, Tahoe, Yukon).

Where To Buy The MAP Sensor And Save

It's important that you avoid buying a cheap knock-off MAP sensor that may cause the MAP sensor problem to reappear.

The following links will help you comparison shop for the original equipment (OE) AC-Delco MAP sensor. The other two sensors are from two well-known automotive brands: Standard Motor Products and Delphi brands:

NOTE: The above manifold absolute pressure (MAP) sensor fit the 1999-2006 V8 Chevrolet Silverado (Suburban, Tahoe) and GMC Sierra (Yukon, Yukon XL).

More Silverado, Suburban, Tahoe, Sierra, And Yukon Tutorials

You can find a complete list of V8 Chevrolet Silverado (Suburban, Tahoe) and GMC Sierra (Yukon, Yukon XL) tutorials in this index:

• GM 4.8L, 5.3L, 6.0L Index Of Articles.

Here's a small sample of the tutorials you'll find in the index:

• Resistance Specifications Of The TAC Electronic Throttle Body.
• How To Test The GM Accelerator Pedal Position (APP) Sensor 2.
• How To Test The MAF Sensor (GM 4.8L, 5.3L, 6.0L, 8.1L).
• Blown Head Gasket Test (GM 4.8L, 5.3L, 6.0L).